Apparatus for sanding and grinding operations utilizing endless abrasive belts are widely used for treatment of surfaces of metal articles, and for surface dressing and dimensioning of lumber. Specifically, in the dimensioning of lumber, abrasive sanding is frequently utilized to provide dimensional stability, and also to control and eliminate modest bowing or warping of dimensioned lumber. When significant material removal is required, and particularly significant material removal of pine or other materials heavy in resinous substances such as pitch, the surface of the belts become loaded with material, thus reducing the effectiveness of the abrasive material to remove material from the work.
In the past, various apparatus and techniques have been utilized to remove adhering particles from the surface of abrasive belts. Such apparatus and techniques include the continuous application of compressed air, or combinations of air and liquid, such as air-water mixtures. In certain other structures, material removal from abrasive belt surfaces may be attempted by exposure of the belt surface to modest vacuum.
As is conventional in abrasive sanders or grinders, stock removal is achieved by utilizing either one or more abrading heads acting upon the exposed surface of the work. Typically, in the dressing and dimensioning of lumber, opposed abrading heads may be utilized, with conveyors acting upon the work so as to move the work into contact with the abrading heads. Typically, each abrading head includes a working surface such as a contact drum or platen supporting the abrasive belt along with a remotely positioned belt tensioning idler roller or drum, the rolls being mounted for rotation about parallel axes. Typically, the idler roll may further include means for maintaining constant tension in the belt, and also means for controlling the axial positioning of the belt on the rollers.
In applying a continuous flow of compressed fluid such as compressed air onto the surface of the belt, excessive quantities of the compressed fluid are required. It has been found that removal of adherent particles is enhanced if intermittent pulses of compressed fluid such as air are applied to the belt rather than a continuous flow. In other words, it appears that removal of adherent material may be improved if the quantity of such adherent material is permitted to build up modestly prior to removal. Shroud means are provided to envelop substantially the entire length of the belt, thereby reducing discharge of dust into the ambient.